Beirut/Calexico, Roundhouse, London

At first glance, the union of Beirut and Calexico is an obvious one. Both bands have imaginations fired by cultures beyond their own; both are besotted by brass. But while one is looking to convert the crowd, the other is hoping to convince them.

Zach Condon is the precocious magpie who stole the sparkly best of Balkan music for Beirut's acclaimed debut Gulag Orkestar. Wearing a black hoodie and white T-shirt, the Albuquerque kid looks like he has just stepped off the set of The OC, but his voice, like his control of his nine-piece band, is way beyond his tender years.

He chants like an orthodox priest and croons like Stephin Merritt of the Magnetic Fields, pausing only to add his trumpet to the thrilling tangle of accordion, violin, mandolin and ukulele. Beirut leave us on a high, quickly followed by a Calexico comedown. The Tucson stalwarts start quietly with the ponderous rock of Yours & Mine, taken from new album Garden Ruin; one that has seen them swap their mariachi horns for pedal steel and electric guitar.

But they don't shy away from their Mexican influences for long. Singer Joey Burns is soon yahooing all over Across the Wire, and Jacob Valenzuela sings Ojitos Traidores with heartfelt passion. Calexico's new taste for driving rhythms and middling solos cause them to melt into the background, but their talent for Ennio Morricone-influenced drama pulls them through.

Then Burns invites Beirut to join Calexico for an astonishing take on Crystal Frontier. The song springs from an exhilarating horn-stamped hoedown and as Burns prolongs the tension, inciting his "personal Jesus" and "my sweet Lord", both bands have their prayers answered.

· Beirut play the Luminaire, London NW6, (020-7372 7123) on Sunday.